Plastic syringe plunger



Filed May 14, 1954 M51. 1 1 5/MM0N05, I INVENTOR.

BY Q

ATTORNEY.

Unite Stat PLASTIC SYRINGE PLUNGER Melvin Simmonds, Los Angeles, Calif., assignor, by direct and mesne assignments, to American Medical Products Corporation, Houston, Tex., a corporation of Texas Application May 14, 1954, Serial No. 429,796 11 Claims. (Cl. 128218) This invention relates to a hypodermic syringe of plastic material and more particularly to a molded syringe barrel of relatively; non-flexible plastic material and a cooperable hypodermic syringe plunger integrally molded from a relatively flexible plastic material.

Prior proposed hypodermic syringes have included a syringe barrel and plunger made of glass, the barrel and the plunger being ground and mated so as to provide a very accurate fit therebetween. Such glass syringes had virtually no leakage and the seal of mated plungers and barrels was generally very good. However, such glass syringes include certain disadvantages. For example, the glass barrels and plungers are subject to breakage during manufacture and in use and therefore were required to be handled very carefully. In addition, such glass plungers are generally not interchangeable with barrels to which they had not been mated. Such glass syringes were very expensive to make and the cost of cleaning and sterilizing glass syringes is high.

Other prior proposed hypodermic syringes have included syringe barrels and plungers made of plastic material. Such plastic syringes have included various designs of a plunger in order to provide an efiective, non-leaking seal between the plunger and the barrel. In one instance, a substantially cylindrical plunger is provided with a forwardly facing and outwardly flaring skirt. Such a skirt contacts the barrel over substantially wide area and it has been found that such a construction of a plunger does not provide effective aspiration of fluid into the syringe barrel. Other plungers of plastic material have included a plurality of longitudinally spaced rings carried by the plunger. When such a plunger is inserted into a barrel, the rings are slightly compressed so that again a circular contact of substantial area is provided between the barrel and the plunger rings. Such an area contact has presented certain difficulties in that there is a tendency for leakage to develop after use and it is diflicult to accurately measure the quantity of fluid drawn into the barrel because the wide area of contact of the plunger with the barrel is difiicult to align with a selected calibration mark on the syringe barrel. Such prior proposed plastic syringes were diflicult to clean, sterilize, required considerable expense in handling, and aspiration was generally poor.

This invention contemplates a hypodermic syringe of plastic material which is so designed and constructed that effective aspiration and ejection of fluid from the syringe is provided, virtually no leakage of fluid occurs between the plunger and the barrel during ejection, and the syringe can be manufactured so inexpensively that the barrel and plunger may be disposed of after use without incurring a cost for syringes which exceeds the cost of prior proposed syringesand their handling.

Generally speaking, this invention includes a syringe barrel molded from suitable non-flexible plastic material such as styrene. The plunger for the syringe of this invention is made of a relatively flexible plastic material such as polyethylene. The plunger includes a fluted shank 2,902,034 Patented Sept. 1, 1959 portion having a thumb rest at one end thereof and a non-fluted extension at the other end. Integral with the non-fluted extension is a thin wafer-like, flexible, yieldable plunger head which is provided with a circumferential edge face adapted to contact internal cylindrical surfaces of the syringe barrel along longitudinally spaced circular lines of contact. The construction of the wafer-like plunger head results in virtually no leakage between the barrel and the head, provides for effective aspiration and ejection of fluid into and from the barrel, and the amount of fluid drawn into the barrel is readily measured because the linewcontact of the wafer-like head with the barrel can be readily and accurately aligned with calibration marks on the barrel.

It is therefore the primary object of this invention to disclose and provide a hypodermic syringe molded from plastic material which is capable of effectively and accurately aspirating selected quantities of fluid and of ejecting such fluid from the barrel without loss by leakage between the plunger and the barrel.

An object of this invention is to disclose and provide a hypodermic syringe made of plastic material which is inexpensive to manufacture and which may be disposable or discarded after use without exceeding costs of prior proposed syringes.

Another object of this invention is to disclose and provide a novel design and construction of a flexible, fluted syringe plunger including a thin wafer-like plunger head adapted to contact internal surfaces. of a syringe barrel along at least two longitudinal spaced circular lines of contact when under the influence of pressure.

A further object of this invention is to disclose and provide a plunger for a hypodermic syringe which is smoothly operable in a syringe barrel and which provides an effective seal with the syringe barrel upon both aspiration and ejection of fluid therefrom.

These and other objects of this invention 'will be readily apparent from the following description of the drawings in which an exemplary embodiment of this. invention is shown.

Fig. l is a side view, partly in section, of a syringe barrel and plunger embodying this invention, the section being taken in a plane bisecting the barrel.

Fig. 2 is an enlarged fragmentary sectional view of the plunger shown in Fig. 1.

Fig. 3 is a transverse sectional view taken in the plane indicated by line III-III of Fig. 2.

Fig. 4 is a transverse sectional view taken in the plane indicated by line IV-IV of Fig. 2.

The hypodermic syringe of plastic material of this invention includes a syringe barrel 10 of well known form and a syringe plunger 11 adapted to be slidably received within the syringe barrel for drawing fluid thereinto and for ejecting the fluid therefrom.

The syringe barrel 10 is preferably molded of a suitable, relatively non-flexible plastic material such as styrene. The syringe barrel includes a cylindrical hollow body portion 12 having a relatively thin uniform wall section. At one end, the body portion 12 is provided with an integral ported nipple 13 adapted to be received within the head of a hypodermic needle associated therewith. At the other end of a body portion 12., the barrel includes radially outwardly extending flange portions 14 affording a finger hold. The outer surface of the cylindrical body portion may be provided with a plurality of calibration marks or indicia 15 for indicating quantity of fluid in the syringe barrel. The internal cylindrical surface 16 of the barrel is so molded that from the nipple end to a point adjacent the thumb rest, the cylindrical surface 16 is virtually uniform in diameter.

The plunger 11 is preferably made from a relatively flexible plastic material such as polyethylene. It has been found that reclaimed polyethylene affords desirable characteristics for molding of the plunger 11 and for giving the plunger 11 desired flexibility and yieldability. The plunger 11 includes a longitudinally fluted shank portion 13 which comprises an inner cylindrical core 19 of selected diameter and integral therewith lonigtudinally extending ribs 20 extending for substantially the entire length of the core 19. The longitudinal ribs 20 may be spaced apart approximately 90 and may have an outer diameter substantially greater than the diameter of the inner core 19. At one end, the shank portion 11 is integrally formed with a circular thumb rest 21 of any suitably selected diameter. The ends of each of the longitudinal ribs 20 may integrally merge with the circular thumb rest 21.

At the other end of the fluted shank portion 11 is provided an integral cylindrical extension 22 having a diameter slightly greater than the diameter of core 19 but less than the diameter of the ribs 20. The ends of the ribs 20 merge and terminate with the inner portion of the cylindrical extension 22.

Integral with the outer end of the cylindrical extension 22 is a wafer-like plunger head 24. In Fig. 2 the wafer-like plunger head 24 is enlarged and the shape thereof is exaggerated so as to more clearly illustrate and show the construction of said plunger head. The head 24 includes a front face having a circumferential marginal portion 25 lying in a plane perpendicular to the axis of the plunger. Inwardly of the marginal portion 25, the front face of the head 24 is slightly dished or concave in form as at 26. The plunger head 24 is provided with a circumferential edge face 27, said circum ferential edge face being of slightly concave configuration so as to provide a front circular edge 28 and a rear circular edge 29. The depth of the wafer-like head 24 may be, for example, .040 inch. The head 24 also includes an annular slightly undercut rear face portion 30 which joins rear edge 29 with the extension 22. The diameter of the circular front and rear edges is slightly greater, approximately .002 inch than the inner diameter of the internal surfaces 16 of the barrel.

It should be noted that the width of the rear annular face portion 30 on the wafer-like head is preferably greater than the thickness or depth of the circumferential edge face 27 and should not be of less width than the depth of said edge face. This construction provides a flexible annular flange-like means which is integrally joined to the cylindrical extension 22 by a section of flexible material which is of slightly less thickness than but more than one-half the distance of the spacing between the front and rear edges 28 and 29 of the waferlike head, said reduction in thickness being caused by the concavity 26 in the front face of the head and by the undercut rear face portion 30. It will be noted that such construction of the Wafer-like head when formed as an integral portion of the cylindrical extention 22 which is of substantially less diameter than the diameter of the head and has an axial length greater than the axial length of the edge face 27 of the head provides a plunger head having maximum flexibility and adaptability to maintain effective sealing contact with the internal cylindrical surfaces 16 of the syringe barrel. The adaptability of the wafer-like head to the internal surfaces of the barrel is further enhanced by the fact that the shank portion of the plunger is out of contact with the internal surfaces of the barrel throughout the operative length of the barrel.

It should be noted that the head 24 lies in a transverse planar zone perpendicular to the axis of the shank portion 18 or the plunger 11 and defined by the transverse planes passing through the edges 28 and 29 of the circumferential edge face 27. It should be noted that in Wardly of the circumferential edge face 27 the material of the plunger head lies within said zone and is of reduced section. The material of the head 24 between or in- 4 wardly of the transverse planes passing through the edges 23 and 29 may form a reduced section due to the relief of material as by the concavity of the rear face 30 or the concavity of the front face 25 disposed about a medial plane of the planar zone. This reduced section provides flexibility and facilitates the establishment of a seal with the surface of the syringe barrel, especially when the plunger is moved outwardly of the barrel as in aspiration.

The concavity 26 of the front face, of the circumferen tial edge 27, and of the undercut, annular face portion 34) results from shrinkage of the plastic material upon cooling in a mold. The shrinkage is such that when the plunger 24 is received within the barrel 10, the front circular edge 28 and the rear circular edge 29 normally contact internal surface portions 16 of the barrel along longitudinally spaced lines of contact.

When the plunger is moved away from the nipple end of the barrel for aspirating fluid thereinto, the rear'circular edge 29 readily and effectively provides a circular line contact with the internal cylindrical surfaces of the barrel. When the plunger 11 is moved toward the nipple end of the barrel as for ejection of fluid therefrom, the flexible, wafer-like head under pressure causes the front circular edge 28 to effectively seal against the cylindrical surfaces of thebarrel. Because the circular line contact is a fine thin line of contact, it will be readily apparent that extremely accurate amounts of fluid may be measured by the alignment of such a thin line of contact with a calibration mark on the barrel. Since there is virtually no leakage between the circumferential edge face 27 of the wafer-like head and the cylindrical surfaces of the barrel, the entire measured amount of fluid is ejected from the barrel.

It will be noted that in operation of the wafer-like plunger head that upon ejection of fluid from the barrel the pressure of the fluid against the flexible flowable material of the thin wafer-like head urges the material of the head to move in an outward direction so that the front circular edge 28 is pressed against the internal cylindrical surfaces of the barrel. The particular construction of the wafer-like head as described above facilitates the flow of material in the Wafer-like head towards thecylindrical surfaces 16 of the barrel, and upon longitudinal movement of the plunger to eject fluid from the barrel such flow of material in the wafer-like head urges the front circular edge 28 into an effective, complete sealing contact with the barrel. Upon aspiration of fluid into the barrel the construction of the wafer-like head also facilitates the flow of the material thereof outwardly toward the surfaces of the barrel so that an effective seal is provided for producing the necessary vacutun in the barrel in front of the wafer-like head for aspirating fluid into the barrel.

It should be noted that the construction of the plunger 11 of this invention provides a flexible, yieldable waferlike plunger head for cooperable sliding and sealing engagement with the internal surfaces of a syringe barrel. The flexible cylindrical extension between the wafer-like head and the longitudinally reinforced shank permits the wafer-like head to properly engage the internal surfaces of the barrel. It may be noted that the fluted shank portion does not contact the internal surfaces of the barrel throughout its entire length, any such contact with the barrel being had at the open end of the barrel adjacent the thumb rest. Even when the fluted shank portion is so misaligned with the axis of the barrel, the flexible construction of the plunger prevents misalignment of the wafer-like head with the axis of the barrel and thereby contributes to the maintenance of an effective seal. Because the contact of the wafer-like head isalong fine thin longitudinally spaced circular lines of contact, the plunger is smoothly slidable along the internal surfaces of the barrel and thereby aifords a smoothly operable hypodermic syringe.

It will be understood that various modifications and changes may be made in the construction of the integral syringe plunger described above, and all such changes and modifications coming within the scope of the appended claims are embraced thereby.

I claim:

1. In combination with a syringe barrel of relatively nonflexible plastic material: an integral plunger of flexible plastic material slidably positioned Within said barrel comprising a circular wafer-like head having a circumferential edge face configured to contact internal surfaces of said syringe barrel along longitudinally spaced thin lines of contact; and means integral with said wafer-like head and flexibly joined thereto at a central portion thereof for supporting said wafer-like head for movement longitudinal of said barrel, said wafer-like head lying within a planar zone transverse to said plunger and defined by said circumferential edge face and including a reduced section of material disposed about a medial plane of said zone, said supporting means having an outer transverse dimension substantially less than the diameter of said wafer-like head whereby said supporting means is normally out of contact with said syringe barrel.

2. In a combination as defined in claim 1 wherein said means for supporting said wafer-like head includes a cylindrical extension of less diameter than said head and integrally joined thereto at the central portion of said head.

3. In combination with a syringe barrel of relatively nonflexible plastic material; an integral plunger of flexible plastic material slidably positioned within said barrel and comprising a circular Wafer-like head having a circurnferential edge face configured to contact internal surfaces of said syringe barrel along longitudinally spaced thin lines of contact; and means integral with said waferlike head and flexibly joined thereto at a central portion thereof for supporting said wafer-like head for movement longitudinal of said barrel, said supporting means having an outer transverse dimension substantially less than the diameter of said wafer-like head whereby said supporting means is normally out of contact with said syringe barrel, said supporting means for said wafer-like head including a cylindrical extension integrally joined to the central portion of said Wafer-like head and a longitudinally fluted shank portion integral with said cylindrical extension.

4. A relatively flexible integral plunger for a syringe barrel comprising: a longitudinal shank portion; an extension on said shank portion; and a circular wafer-like plunger head carried at the free end of said extension and projecting transversely beyond said extension in a plane lying perpendicular to the axis of the shank portion; said wafer-like head including a front face having a circumferential marginal face portion lying in a plane perpendicular to the axis of the shank portion, said front face Within said marginal portion being concave, a circumferential edge face having a concave configuration defining a front circular edge and a rear circular edge, and an annular rearwardly facing portion of concave configuration joining said rear circular edge with said extension whereby said wafer-like head is flexibly adaptable to maintain sealing contact with surfaces of a syringe barrel.

5 A plunger as stated in claim 4 wherein the width of said rearwardly facing portion is greater than the depth of said circumferential edge face.

6. A relatively flexible integral plunger for a syringe barrel comprising: a longitudinal shank portion; an extension on said shank portion; and a circular wafer-like plunger head carried at the free end of said extension and projecting transversely beyond said extension in a planar zone lying perpendicular to the axis of the shank portion; said wafer-like head including a circumferential edge face configured to contact internal wall surfaces of the barrel on longitudinally spaced circular lines; said head including a reduced section inwardly of said edge face and spaced from planes defining said transverse zone.

7. A relatively flexible integral plunger for a syringe barrel comprising: a longitudinal shank portion; an extension on said shank portion; and a circular wafer-like plunger head carried at the free end of said extension and projecting transversely beyond said extension in a planar zone lying perpendicular to the axis of the shank portion; said wafer-like head including a circumferential edge face having front and rear circumferential edges for circular line contact with internal surfaces of the barrel; said planar zone being defined by transverse planes passing through said front and rear circumferentially edges, said head including a reduced section spaced inwardly from said transverse planes.

8. A relatively flexible integral plunger for a syringe barrel comprising: a longitudinal shank portion; an extension on said shank portion; and a circular wafer-like plunger head carried at the free end of said extension and projecting transversely beyond said extension in a plane lying perpendicular to the axis of the shank portion; said Wafer-like head including an undercut rear portion joining a rear circular edge of said head with said extension.

9. A plunger construction comprising a longitudinal shank and a wafer-like plunger head carried by said shank and integral therewith, said shank and said wafer-like head being of flexible, elastic plastic material, said waferlike head having an annular flange means integrally joined to said shank by a reduced section of material having less thickness than the thickness of said flange at the circumferential margin of said head, said head having a circumferential edge face providing longitudinally spaced edges for contact with a cylindrical surface; said annular flange means lying between spaced transverse planes passing through said longitudinally spaced edges, said reduced section of material lying between and spaced from said planes.

10. A plunger construction comprising: a longitudinal shank and a circular plunger head carried by said shank and integral therewith, said shank and said head being of flexible material, said head including an annular flange means integrally joined to said shank and lying in a transverse zone defined by spaced planes passing through circumferential edge margins of said flange means, said flange means including a reduced section of material adjacent to the joining of said flange means to said shank, said reduced section lying centrally between said planes.

11. A plunger construction comprising: a longitudinal shank and a circular plunger head carried by said shank and integral therewith, said shank and said head being of flexible material, said head including an annular flange means integrally joined to said shank and having circumferential spaced edge margins, said flange means including a reduced annular section of material disposed between the said circumferential edge margins of said flange means and said shank.

References Cited in the file of this patent UNITED STATES PATENTS 2,102,704 Hein Dec. 21, 1937 2,619,087 Oclassen et a1 Nov. 25, 1952 2,666,434 Ogle Ian. 19, 1954 2,671,449 Dann Mar. 9, 1954 2,695,612 Fields Nov. 30, 1954 2,724,385 Lockhart Nov. 22, 1955 

